1. Field of the Invention
The present invention relates to a photo printer, and more specifically, to a photo printer which is operated with a constant angular velocity, capable of registering the used color of the ribbon, and capable of detecting the amount of the ribbon used.
2. Description of the Prior Art
Along with the development of digital cameras, photo printers, which are able to print photos directly, become popular.
Please refer to FIG. 1 in conjunction with FIG. 2. FIG. 1 is a schematic diagram of a color printer 10 according to the prior art. FIG. 2 is a cross-sectional view of the printer 10 depicted in the FIG. 1 along the line 2—2. The color printer 10 can be a photo printer for printing photos. The printer 10 comprises a ribbon 20, a light source 22, a photo sensor 24, a heat printhead 26, and a controller 30. The ribbon 20 is rotatable in a ribbon-driving device (not shown in FIGS. 1 and 2). The controller 30 is used for registering the position of the ribbon 20 in order to control the printer 10 in operation.
Please refer to FIG. 3. FIG. 3 is a schematic diagram of the ribbon and the photo sensor structures in the printer 10. The ribbon 20 contains a plurality of dye regions 40 in order. Each dye region 40 contains dye frames 32, 34, 36, 38 with different colors, such as the dye frame 32 with yellow; the dye frame 34 with magenta; the dye frame 36 with cyan; and the dye frame 38 being an over-coating. Each yellow dye frame 32 is equipped with a black bar region 44 in the front. Moreover, a transparent separation region 45 without any color is located between each of the dye frames 32, 34, 36, 38. The black bar region 44 and the transparent separation region 45 are used for distinguishing each start position of the dye frames 32, 34, 36, 38 by using the controller 30. The lengths of the dye frames are much longer than those of the black bar region 44 and the transparent separation region 45.
As shown in FIG. 3, after the light source 22 irradiates the ribbon 20 with the beam 25, the photo sensor 24 senses the beam 25 penetrating the dye region 40 and generates corresponding sensing signals. Because of different penetrability of the dye frames 32, 34, 36, 38, and the black bar region 44 to the beam 25, the photo sensor 24 generates different sensing voltages when passed by two adjacent dye frames one after another. The controller 30, however, registers the positions of the dye region 40 and the dye frames 32, 34, 36, 38 in the dye region 40 according to the keeping time of the sensing voltage generated by the photo sensor 24. And the heat printhead 26 is used to transfer the dye of the ribbon 20 onto a medium.
Because the controller 30 can determine which dye frame is passing due to different penetrability of each dye frame in the dye region 40, the controller 30 is able to register the positions of the dye frames 32, 34, 36, 38 on the dye region 40 of the ribbon 20 by distinguishing four different sensing voltages. However, the yellow dye frame 32 generates the same sensing voltage with the over-coating dye frame 38. As a result, the controller 30 is required for discerning the order of the other two dye frames (the magenta dye frame 34 and the cyan dye frame 36) to distinguish the yellow dye frame 32 from the over-coating frame 38. The other way is arrange specific bar codes in the front of the yellow dye frame 32 and the over-coating dye frame 38 to distinguish between them. Except determining the amount of the dye region 40 of the ribbon 20, the controller 130 is only able to determine the positions of each dye frame in the dye region 40. After running out of the ribbon 20, if the printer 10 is still used without replacing the ribbon 20, the printer is likely to cease printing in the printing process and bewilder users.